The most efficient heat engines to date, Stirling engines, invented 200 years ago, lose 30% efficiency because they expand and compress their internally cycling working fluid from the volumes incasing their heating and cooling exchangers, and hence their fluid is heated and cooled isothermally during the stroke so that some of the added heat cannot be fully converted to their full work output potential.
Ever since, thermodynamic specialists have sought ways to retrieve the balance. The Second Law states that heat always flows from a higher to a lower level. Some specialists have confused this quest by interpreting the Second Law of Thermodynamics to mean a fluid cannot be cycled from a low to a high energy level. In fact, to be adiabatic, a bolus of cycled working fluid must be cycled to a higher level before being batched and expanded. The Soony engine does not pass its heat from a low to a high level, breaking the Second Law. Rather its working fluid cycles from a balanced low pressure environment to a balanced high pressure environment much like a boat passes through a canal lock. When raised, the raised level is used to power the next downstroke. After cycling, heat is added to the cycled fluid from an outside source.
Hundreds of billions of dollars worth of heat energy could be converted into electricity every year, if a cost efficient heat-driven generator were developed. The Carnot principle indicates that a set amount of energy is available within a given temperature range for heat to power conversion if a way can be found to use it.